1. Field of the Invention
The present general inventive concept relates to an inkjet printhead, and more particularly, to a heating structure to improve performance of an inkjet printhead and a thermal inkjet printhead including the heating structure.
2. Description of the Related Art
An inkjet printhead is a device to print a predetermined color image by ejecting minute droplets of ink on a desired area of a printing paper. Inkjet printheads can be generally classified into two types according to the ejection mechanism of ink droplets. The first type is a thermal inkjet printhead that ejects ink droplets using the expansion force of ink bubbles created using a heat source, and the second type is a piezoelectric inkjet printhead that ejects inkjet droplets using a pressure created by the deformation of a piezoelectric element.
The ejection mechanism of ink droplets of the thermal inkjet printhead will be described in detail. When a pulse type current is applied to a heater composed of heating resistors, ink around the heater is instantly heated to approximately 300° C. Thus, the ink boils and bubbles are generated. Then, pressure is applied to the ink filled in an ink chamber by the expansion of the ink bubbles. As a result, ink droplets are ejected to the outside from the ink chamber through the nozzles in a droplet shape.
FIG. 1 is a cross-sectional view illustrating a conventional thermal inkjet printhead. Referring to FIG. 1, the conventional thermal inkjet printhead includes a substrate 10 on which a plurality of material layers are formed, a chamber layer 20 stacked on the plurality of material layers, and a nozzle layer 30 stacked on the chamber layer 20. A plurality of ink chambers 22, in which ink that is to be ejected is filled, are formed in the chamber layer 20. A plurality of nozzles 32 through which ink is ejected are formed in the nozzle layer 30. An ink feed hole 11 for supplying ink to the ink chambers 22 is formed in the substrate 10. Also, a plurality of resistors 24 that connect the ink chambers 22 and the ink feed hole 11 are formed in the chamber layer 20.
An insulating layer 12 for insulating a plurality of heaters 14 from the substrate 10 is formed on the substrate 10. The insulating layer 12 may be formed of silicon oxide. The heaters 14 are formed on the insulating layer 12 to generated ink bubbles by heating ink. Electrodes 16 are formed on the heaters 14. A passivation layer 18 for protecting the heaters 14 and the electrodes 16 is formed on surfaces of the heaters 14 and the electrodes 16. The passivation layer 18 may be formed of silicon nitride, silicon oxide, aluminum nitride or aluminum oxide. Anti-cavitation layers 19 for protecting the plurality of heaters 14 from a cavitation force generated when ink bubbles disappear are formed on the passivation layer 18. The anti-cavitation layer may be formed of tantalum Ta.
However, in the inkjet printhead having the above structure, since the passivation layer 18 formed on the heaters 14 is formed of a material having very small thermal conductivity, lots of heat generated from the heaters 14 is accumulated in the passivation layer 18 rather than being transmitted to ink in the ink chambers 22. Accordingly, the thermal efficiency of the heaters 14 may deteriorate, and a large amount of input energy for generating bubbles is required. In addition, the heat accumulated in the passivation layer 18 increases the temperature of the ink in the ink chambers 22 to change the viscosity of the ink, and thus the ejecting property of the inkjet printhead may deteriorate.